[inspector] migrate stepping related methods to debug-interface

src/inspector/debugger_script_externs.js

 // Copyright 2016 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 /** @typedef {{
         type: string,
         object: !Object,
         name: (string|undefined),
         startLocation: (!RawLocation|undefined),
         endLocation: (!RawLocation|undefined)
@@ skipping 43 matching lines @@
         isAtReturn: boolean,
         details: function():!JavaScriptCallFrameDetails
     }} */
 var JavaScriptCallFrame;
 
 /**
  * @const
  */
 var Debug = {};
 
-Debug.clearStepping = function() {}
-
 Debug.clearAllBreakPoints = function() {}
 
 /** @return {!Array<!Script>} */
 Debug.scripts = function() {}
 
 /**
  * @param {number} scriptId
  * @param {number=} line
  * @param {number=} column
  * @param {string=} condition
@@ skipping 109 matching lines @@
 /** @interface */
 function BreakEvent() {}
 
 /** @return {!Array<!BreakPoint>|undefined} */
 BreakEvent.prototype.breakPointsHit = function() {}
 
 
 /** @interface */
 function ExecutionState() {}
 
-/** @param {!Debug.StepAction} action */
-ExecutionState.prototype.prepareStep = function(action) {}
-
 /**
  * @param {string} source
  * @param {boolean} disableBreak
  * @param {*=} additionalContext
  */
 ExecutionState.prototype.evaluateGlobal = function(source, disableBreak, additionalContext) {}
 
 /** @return {number} */
 ExecutionState.prototype.frameCount = function() {}
 
@@ skipping 300 matching lines @@
 ScopeMirror.prototype.setVariableValue = function(name, newValue) {}
 
 /**
  * @interface
  * @extends {Mirror}
  */
 function ContextMirror() {}
 
 /** @return {string|undefined} */
 ContextMirror.prototype.data = function() {}